In a traditional enterprise network communication solution, PBX or Internet Protocol private branch exchange (IP PBX) devices occupy a large proportion. The methods of PBX/IP PBX for accessing a public switched telephone network (PSTN: Public Switched Telephone Network) or next generation network (NGN: Next Generation Network) include the following: 1) private E1/T1 line; 2) basic rate access (BRA: Basic Rate Access) or integrated services digital network (ISDN: Integrated Services Digital Network) private line; 3) analog subscriber line; 4) H.323 IP relay; 5) session initiation protocol (SIP: Session Initiation Protocol) relay. A traditional PBX device is in an interworking relationship with a public network. The operator network provides enterprise PBXs with a method for accessing the public network, and seldom provides additional services for PBX devices.
With the fast development of Internet Protocol multimedia subsystem (IMS: IP Multimedia Subsystem), the traditional enterprise PBX solution also evolves toward the IMS network. The telecommunications and Internet converged services and protocols for advanced networking (TISPAN: Telecommunications and Internet converged Services and Protocols for Advanced Networking) defines two PBX access methods: 1) accessing the IMS via a user-network interface (UNI: User-Network Interface); 2) accessing the IMS via a network-network interface (NNI: Network-Network Interface). The former is a subscription-based method for accessing the IMS network, and enables the IMS network to provide various value-added services for a PBX user. The latter regards a PBX as a peer network for accessing the IMS, where the IMS provides only access for the PBX to the public network, but does not provide additional value-added services.
During evolution of the traditional enterprise PBX solution to the IMS network, as the MS network uses SIP as the basic communication protocol, while the SIP protocol requires that a user must send a registration message so as to acquire the location information about the user, the TISPAN standard introduces a concept of wildcard (wildcard) registration, where one PBX switch only needs to and one registration message, and the IP multimedia public identity (IMPU: IP Multimedia Public Identity) registered by the user and a wildcard IMPU (generally an operator allocates one number segment for use by an enterprise) are presented by means of implicit registration set, thereby solving the registration problem.
As most PBX switches are capable of providing rich services and functions, they do not rely on an application server (AS: Application Server) to provide additional supplementary services. However, it is still necessary to move certain value-added services to the AS due to the restriction on the PBX networking or for the sake of service optimization. A typical example of the restriction of PBX networking is that the PBX may not independently provide fixed mobile convergence (FMC: Fixed Mobile Convergence) applications, but relies on capabilities of the IMS network.
The IMS network uses SIP as the basic communication protocol, and the SIP protocol requires that a user must send a registration message so as to acquire the location information about the user. Therefore, a PBX user that implements independent services must register before successfully initiating a call. As such, if certain PBX users hope to implement respective independent supplementary services, they need to independently open an account in the IMS domain, and must independently register. Therefore, the PBX is required to initiate registration flows for multiple users, increasing the handling load of network elements, and bringing additional work to the PBX switch, which does not comply with the operation rules for an enterprise PBX.